Sheet sensor

ABSTRACT

Apparatus which inactivates a xerographic machine in response to a copy sheet miss-puff. A sheet of paper remaining on the xerographic drum beyond the stripping station will move beneath a pneumatic sensor head. A second pneumatic sensor head adjacent the edge of the drum at an area beneath which misfed sheets will not pass is pneumatically coupled with the first sensor so that a change of pressure between the two sensors, as caused by a misspuffed sheet, will cause the tripping of a fluidic switch to energize a control relay and stop the machine.

United States Patent X 6 6 H 5 7 l 2 7 2 mmm mT.m WA

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Filed Sept. 8, 1969 n 0 Mn 1 o 7M N 9 l 4 1x5 .mhv mew XR de mm 8 i tsas PA ll. 53 47 [.l

Primary Examiner-Joseph Wegbreit Assistant Examiner-Bruce H. Stoner, Jr.

AnorneysNorman E. Schradcr, James J. Ralabate and Michael J. Colitz. Jr.

[54] SHEET SENSOR $Clalms,6Drawlng Figs. ABSTRACT: Apparatus whichinactivates a xerographic machine in response to a copy sheet miss-puff.A sheet of paper remaining on the xerographic drum beyond the strippingstation will move beneath a pneumatic sensor head. A second pneumaticsensor head adjacent the edge of the drum at an area beneath whichmisfed sheets will not pass is pneumatically coupled with the firstsensor so that a change of pressure between the two sensors, as causedby a miss-puffed sheet, will cause the tripping of a fluidic switch toenergize a control relay and stop the machine.

66 4 X 17. 7 H 5/ 7 mm 2 2 m: m "n" N" m: m mmm w m nu n an .IPL mmm M a"n" I m: cTe nu" Aw m: "T "n" SM nu" QDK m: mTm n3 2 N a U9 Ia H L 9 u 0h UhF m m 2 0 6 in UB5 U 3 PATENTED DEC 1 4 Ian SHEET 1 [IF 2 INVENTOR.THOMAS S. SPINELLI BY V SHEET SENSOR This invention relates to a sensingdevice for detecting sheet material. More particularly, this inventionrelates to a device for monitoring a moving photoconductive surface andfor inactivating its movement upon the detection of a sheet moved intoproximity to detection apparatus.

In the practice of xerography, as described in U.S. Pat. No. 2,297,691to Chester F. Carlson, a xerographic photoconductive surface comprisinga layer of photoconductive insulating material affixed to a conductivebacking is used to support electrostatic images. In the usual method ofcarrying out the process, the xerographic surface is electrostaticallycharged unifonnly over its surface and then exposed to a light patternof the image being reproduced to thereby discharge the charge in theareas where light strikes the layer. The undischarged areas of the layerthus form an electrostatic charge pattern in conformity with theconfiguration of the original light pattern.

The latent electrostatic image can then be developed by contacting itwith a finely divided electrostatically attractable material such astoner powder. The powder is held in image areas by the electrostaticcharge pattern on the layer. Where the charge field is greatest, thegreatest amount of material is deposited; where the charge field isleast, little or no material is deposited. Thus a powder image isproduced in conformity with the light image of copy being reproduced.

A sheet of paper or other suitable support material may then be broughtinto contact with the photoconductive surface in registration with theimage thereon. The powder may be transferred to the support material byelectrostatic means behind the support material. The electrostatic meanswill electrostatically transfer the toner material from thephotoconductive surface to the support material. The electrostatic forceconcurrently induces a charge into the support material tending toelectrostatically tack the support material to the photoconductivesurface. The support material may then be stripped from thephotoconductive surface, as by a pneumatic puffer which blows a sharpstream of air between the paper and drum and physically forces thebacking sheet away from the photoconductive surface. The toner image maythen be fixed to the support material to form a pennanent copy of theoriginal document being reproduced.

Occasionally, a sheet of paper will adhere to the drum surface past theposition at which it should have been removed. This occurs when thepuffer mechanism fails to operate, the paper is not aligned in theproper position on the photoconductive surface, when a double sheet isfed into the transfer station, or the like. When this situation occurs,it is desirable to detect or sense the misfed sheet on thephotoconductor and immediately inactivate the machine. If the machinedoes not shut down immediately, the jamming of paper within the machineor the dumping of developer from the developer housing may occur. Thesecause downtime or damage to the machine.

Several devices have been employed to detect a copy sheet on thephotoconductive surface beyond the point at which it should have beenremoved. In one approach to the problem, as defined in U.S. Pat. No.3,360,652, to Tayeb Bemous, apparatus is disclosed for reflecting lightfrom a source of illumination onto the photoconductive surface beyondthe sheet stripping means. The light reflecting from the photoconductivesurface will enter a photocell to retain the machine in an operativestate. If, however, a sheet is misfed and moves into a position beneaththe light source and photocell, the photocell will sense a variation inthe reflected light and inactivate the machine in response thereto.

ln another approach to the problem, as for example, described in U.S.Pat. No. 3,30l,975, to Raymond H. Camp, et al., a mechanical finger ispositioned to ride against the photoconductive surface. If a sheet ofpaper is not removed from the drum by the pufier, the sheet of paperwill strike the finger, pivoting it, to thereby trip a switch to thusinactivate the device.

While devices of these types operate satisfactorily and are incommercial use today, neither may be considered a universal typedetector for misfed sheets. By way of example, the mechanical finger ofthe Camp et al. device requires an element to be in physical contactwith the photoconductive surface at all times. If this device were usedwith a photoconductive surface of insufficient hardness, it would resultin the creation of a circumferential groove in the photoconductor afterextended use. This is undesirable since it would result in a linearimperfection in the drum as well as to copies transferred therefrom.

The optical misspuff detector of the type described in the Bemouspatent, which relies on light energy reflected from the drum, may resultin a light fatiguing of photoconductors having high spectralresponsiveness. Thus, if the optical miss-puff detector were used incombination with certain photoconductors it would result in the changingof the spectral characteristics of the photoconductive surface along acircumferential line in a manner analogous to that described withrespect to the mechanical miss-puff detector of Camp et al. and resultin similar deficiencies.

To present invention is directed to a device for sensing misfed sheetsof copy which has not been removed from the photoconductive surface atthe sheet-stripping station. The present invention employs laterallydisplaced pneumatic sensor elements coupled together so that a change ofpressure therebetween may be registered as a result of a sensed misfedsheet beneath one of the sensors to inactivate the machine.

It is therefore an object of the instant invention to overcome theabove-noted prior art deficiencies.

It is a further object of the instant invention to control a machine inresponse to a change in pneumatic conditions as registered by monitoringdevices.

It is a further object of the instant invention to detect sheets ofpaper which improperly adhere to a rotating xerographic drum.

lt is a further object of the instant invention to detect sheets beingtransported adjacent sensor members.

These and other objects of the instant invention are attained bypneumatic sensor heads adjacent an area to be sensed with one of thesensor heads positioned beneath the path past which a misfed sheet wouldmove and the second laterally displaced therefrom adjacent an areabeneath which a misspuffed sheet would not pass. The occurrence of amisfed sheet beneath the first sensor head causes a pneumatic imbalancebetween a pneumatic switching means coupling the sensor heads toregister the misfed sheets and to inactivate the sheet beneath themechanism.

For a better understanding of the invention as well as other objects andfurther features thereof, reference is made to the following detaileddescription of the invention to be read in connection with theaccompanying drawings, wherein:

FIG. 1 is an isometric view of a part of a xerographic machine includinga xerographic drum with pneumatic sensor heads positioned thereat;

FIG. 2 is a schematic illustration of the xerographic drum and sensorheads in association with the pneumatic control devices therefor;

FIG. 3 is a side sectional view of a sensor head of HG. 2;

HO. 4 is a schematic illustration of the xerographic drum and sensorheads in association with the pneumatic control devices therefor butemploying an alternate sensor head assembly;

HO. 5 is a sectional view of a sensor head of FIG. 4 taken along line 55thereof; and FIG. 6 is a sectional view taken along line 6-6 of FIG. 5.

As shown in the drawings, a xerographic member in the shape of a drum 10is shown in the position that it would be mounted in an automaticxerographic machine. The drum is rotatably mounted on shaft, not shown,extending through bearing 12 in the middle of the drum. The drum is heldon the shaft by means of a hand nut 14, which cooperates with threads onthe end of the shaft to secure the drum in place.

Sheets of paper are fed by the conveyor 16 into surface contact with thedrum and electrostatically tacked to the drum surface by transfercorotron 18. At this point, xerographic powder images which havepreviously been developed on the drum surface are transferred to thesurface of the sheet of paper by the transfer corotron 18. As the drumcontinues to rotate the sheet of paper is carried by the drum towardsthe conveyor belt 20. The conveyor 20 is a vacuum conveyor which willhold the paper on the surface of the belt and draws the paper away fromthe drum surface after the sheet has contacted the surface of theconveyor.

As the leading edge of the sheet of paper rotates to a position justover the conveyor belt 20, a puffer tube 22 directs a series of sharpstreams of air through nozzles 24 between the drum surface and the sheetof paper. The nozzles 24 extend across the length of the drum andefiectively deflect the sheet of paper from the surface of the drum downagainst the surface of the belt 20. The stream of air in the puffer tube22 emerging from the nozzles 24, is produced by a small air pump, notshown, and controlled and timed by electrical circuitry, not shown, topuff at the proper time to deflect the sheet of paper onto the conveyorbelt. Further details of the pufi'er and other portions of thexerographic machine may be had by reference to US. Pat. No. 3,301,126,issued to Osborne et al.

if for any reason the puffer mechanism fails to strip the sheet of paperfrom the surface of the drum, the sheet of paper would otherwisecontinue to rotate around the drum surface interfering with theoperation of other mechanisms about the periphery of the drum andcausing leakage of developer from its housing. Also, with the sheet ofpaper on the surface of the drum, further xerographic images cannot beproduced or developed. It is, therefore, desirable to immediately stopthe machine and manually remove the sheet of paper from the drumsurface.

For the purpose of detecting sheets not removed from the xerographicdrum by the puffer 22, detector elements in the form of pneumaticsensing heads 30 and 32 as shown in FIGS. 1 and 2 are provided adjacentthe xerographic drum in a location whereby an unpuffed sheet would passbeneath sensor 30. The view of FIG. 2 shows a section of thephotoreceptive plate l0'with the sheet of unpuffed copy paper 28attached thereto in a location beneath the sensor heads. During normaloperating procedures, the copy sheet would not be there and the sensorheads would be the same distance from the photoconductive plate.

The showing of FIG. 2 is also a schematic illustration of the controllogic to sense the presence of a misspuffed sheet. These elements,except for the sensor heads and pneumatic lines thereto are preferablymounted at a location remote from the xerographic surface whereat spaceis at a premium. The pneumatic sensor heads are adapted to be suppliedwith a source of fluid, preferably air, from a pressure source 34, asfor example, the accumulator tank of the xerographic machine. Line 36takes this source of high pressure and distributes it along three majorchannels 38, 40 and 42. Line 38 brings a flow of fluid to the firstsensor head 30 while line 40 directs a flow of fluid to the secondpressure head 32. The third branch line from the source of fluid is line42 which brings air into orifice PS of a pneumatic control device 44 asshown in the form of a Schmitt-Trigger. Schmitt-Triggers arecommercially available devices. Ones employable herein are sold by theCorning Corporation, Corning, New York as part No. 191,448 or 191,456.Also being fed into the Schmitt-Triggers at orifices Cl and C2 is asource of pressure from lines 46 and 48 which draw their pressures as anoffshoot from line 38 and 40 respectively to monitor the flow of fluidtherethrough.

In normal operations, the airflow from the pressure source is adjustedso that sensor heads 30 and 32 are exhausting air through orifices 58 ata common rate with the resulting pressure between C1 and C2 as receivedfrom lines 46 and 48 being equal. In this normal state, the fluid isexhausted from the Schmitt-Trigger 44 through exit orifice 02. Adjustingnuts 50 and 52 on lines 38 and 40 permit the adjustment of the airflowto the sensor heads so that the balanced state of the control device 44may be attained. Brackets 60 and 62 support the heads in their properorientation.

When a miss-puff has occurred and a piece of sheet material is fedbeneath one of the sensor heads 30 by the drum, the airflow therefrommeets a change of resistance due to the change of condition beneath thesensor head. This is registered as an increase of air pressure to theSchmitt-Trigger 44 through line 46 and orifice C1. Sensor head 32 doesnot sense the sheet due to its location to the side of the misfed sheetand this portion of the xerographic drum acts as a reference surface. Inthis state, the pneumatic imbalance in the Schmitt-Trigger betweenpoints Cl and C2 causes pressure to switch its flow and flow fromorifice 01 through line 54. This reverses the state of the controldevice to trip or trigger the pressure switch 56. This, in turn,reverses the state of contact relay CR1 to trigger it and inactivate themachine.

. The fact that the reference surface employed is an edge of thesheet-feeding surface with the pneumatic sensors laterally disposedadjacent the drum permits the sensing of sheet material on the drum eventhrough the drum may not be of a perfect right circular cylinder. Thatis, the distance between the sensor heads and the sheet-feedingphotoconductive surface will cause equal changes of pressure in theevent that the photoreceptive surface is out of round.

1n the alternate embodiment as disclosed in the FIGS. 4-6 showing, thesensor heads 70, 72 are of a slightly modified design. The sensor headsare each constructed to receive two pneumatic lines on the side thereofremote from the sensing side. As in the first embodiment, a suitablesource of fluid 74 provides fluid pressure through line 76 which isdivided between lines 78 and 80 to provide a source of pressure to thesensor head monitoring the movement of sheets on the drum. These linesdirect fluid into the sensor head which is directed into a swirlingfashion to the path to the sensor head and adjacent the area to besensed. A branch, line 82, from line 76 directs air to theSchmitt-Trigger 84 which may be of the same design as that describedwith respect to the FIG. 2 embodiment. Lines 86 and 88 couple anaperture through the center of the sensor heads back to orifices Cl andC2 of the Schmitt- Trigger. Details of the sensor heads will bedescribed hereinafter. The end of these lines adjacent the sensor headsare directed to sense the pressure at the central portion of the sensorhead between the sensor head and the area being sensed. This is at thevortex of the swirling air caused by lines 78 and 80. Adjusting nuts 90and 92 may be provided on line 78 and 80 to adjust the pressures to thesensor heads so that the pressure sensed by C1 and C2 through lines 86and 88 are equal. ln this normal operating state, air is exhausted fromthe control device 84 through orifice 02.

When, however, a foreign object such as a misfed copy sheet passesbeneath one of the sensor heads, 70, this head senses the change ofpressure thereat which is registered at a backup of pressure to C1through line 86. This pneumatic imbalance across orifices Cl and C2causes a flow of fluid through orifice 01 to trigger the pressure switch96, trip the contact CR1 and inactivate the machine.

Details of the pneumatic sensor heads of the FIGS. 4-6 embodiment areshown in FIGS. 5 and 6. Air is adapted to be supplied through line 80into hole 100. This air is channeled to a central circular chamber 102through intermediate passage 104. Air entering the chamber 102 isspiraled due to its construction and relationship to passage 104. Thisair is then passed through connecting passage 106 to a circular exhaustchamber 108 communicating with exterior of the device and facing thearea to be sensed. As the spiraling air passed from chamber 102 tochamber 108, its spiraling is continued. Venting hole 110 connects line88 with the central portion of chamber 102 to monitor the vortex of thespiraling air in the chamber 102 during normal operation. Line 88 whichis the input signal to the Schmitt-Trigger can react very sensitively tochanges beneath the sensor head since it is the vortex of the air whichis being monitored. Both sensor heads 70 and 72 are of this sameconstruction.

In a normal operating state, the pressure source 34 of the firstembodiment would be provided with about pounds per square inch ofpressure while the pressure source of the second embodiment would beprovided with the same pressure. The three lines from the pressuresource would preferably receive about equal fluid flows. The pressureheads of the first embodiment would be positioned about 0.020 inch fromthe xerographic surface, while they would be located about 0.030 inchaway from the xerographic surface in the second embodiment. A sheet ofpaper, nominally 0.003 inch, passed beneath the sensor heads would causea change in pressure across the Schmitt-Trigger of about 0.25 inch ofwater in both embodiments. This pneumatic pressure difference would besufficient to cause the flow of fluid to the pressure switch toinactivate the machine. The existence of miscellaneous foreign objects,as for example, toner particles in the drum which are merely a fewmicrons in thickness, would be insufficient to cause an adequatepressure difference between the sensing portions of the Schmitt-Triggerto register it as a misfed sheet and would therefore not inactivate themachine.

While the instant invention has been described as carried out in thespecific embodiments thereof, it is not intended to be limited therebybut it is intended to protect the invention broadly within the scope ofthe appended claims.

What is claimed is:

1. Apparatus for detecting misfed copysheets on a xerographic surface ofa xerographic reproducing machine and to inactivate the machine inresponse thereto including a first sensor head positioned adjacent thexerographic surface to overlie a portion thereof beneath which misfedsheets may pass to direct a stream of fluid thereagainst,

a second sensor head positioned adjacent the xerographic surface tooverlie a portion thereof beneath which misfed sheets may not pass todirect a stream of fluid thereagainst,

means coupling said sensor heads to detect a pneumatic balance ofpressure between said sensor heads when no material to be detected isbetween said first sensor head and the xerographic surface, saidcoupling means being rendered imbalanced when sheet material is passedbetween said xerographic surface and said first sensor head and controlmeans triggered by said coupling means to inactivate the machine inresponse to said imbalanced condition.

2. The apparatus as set forth in claim 1 wherein said sensor heads areadapted to be laterally disposed adjacent a xerographic drum with saidsecond sensor head adjacent an edge thereof and said first sensor headadjacent a central portion thereof.

3. Apparatus for monitoring sheet material movement along a path oftravel including first and second pneumatic sensor means each adapted todirect a stream of fluid against a reference surface,

means to position said first sensor means adjacent the path of travel sothat sheet material may pass between said reference surface and saidfirst sensor means means to position said second sensor means adjacentsaid first sensor means whereby said second sensor means continues todirect a stream of fluid against said reference surface as the sheetmaterial passes between said first sensor means and said referencesurface,

pneumatic switching means, and

means coupling said first and second sensor means with said pneumaticswitching means and being adapted to normally retain said switchingmeans in a first state and to reverse the state of said switching meansupon a change of condition of sheet material between the referencesurface and said first sensor means.

4. The apparatus as set forth in claim 3 wherein said pneumatic sensormeans include means to supply flows of fluid against said sheet feedingsurface and said reference surface.

5. The apparatus as set forth in claim 4 wherein said coupling meansincludes means to :nonitor the flows of fluid.

1. Apparatus for detecting misfed copysheets on a xerographic surface ofa xerographic reproducing machine and to inactivate the machine inresponse thereto including a first sensor head positioned adjacent thexerographic surface to overlie a portion thereof beneath which misfedsheets may pass to direct a stream of fluid thereagainst, a secondsensor head positioned adjacent tHe xerographic surface to overlie aportion thereof beneath which misfed sheets may not pass to direct astream of fluid thereagainst, means coupling said sensor heads to detecta pneumatic balance of pressure between said sensor heads when nomaterial to be detected is between said first sensor head and thexerographic surface, said coupling means being rendered imbalanced whensheet material is passed between said xerographic surface and said firstsensor head and control means triggered by said coupling means toinactivate the machine in response to said imbalanced condition.
 2. Theapparatus as set forth in claim 1 wherein said sensor heads are adaptedto be laterally disposed adjacent a xerographic drum with said secondsensor head adjacent an edge thereof and said first sensor head adjacenta central portion thereof.
 3. Apparatus for monitoring sheet materialmovement along a path of travel including first and second pneumaticsensor means each adapted to direct a stream of fluid against areference surface, means to position said first sensor means adjacentthe path of travel so that sheet material may pass between saidreference surface and said first sensor means, means to position saidsecond sensor means adjacent said first sensor means whereby said secondsensor means continues to direct a stream of fluid against saidreference surface as the sheet material passes between said first sensormeans and said reference surface, pneumatic switching means, and meanscoupling said first and second sensor means with said pneumaticswitching means and being adapted to normally retain said switchingmeans in a first state and to reverse the state of said switching meansupon a change of condition of sheet material between the referencesurface and said first sensor means.
 4. The apparatus as set forth inclaim 3 wherein said pneumatic sensor means include means to supplyflows of fluid against said sheet feeding surface and said referencesurface.
 5. The apparatus as set forth in claim 4 wherein said couplingmeans includes means to monitor the flows of fluid.